Negative air filtration system

ABSTRACT

A negative air filtration system and a method of operating a negative air filtration system are provided. The negative air filtration system includes a housing, a pre-filter, a HEPA filter, and a fan assembly. The housing including an inlet and an outlet. The pre-filter is disposed within the housing, downstream of the inlet. The HEPA filter is disposed within the housing, downstream of the pre-filter. The fan assembly is disposed within the housing, downstream of the HEPA filter. The fan assembly is in airflow communication with the pre-filter and the HEPA filter. The fan assembly is configured to generate a negative pressure across the pre-filter and the HEPA filter. The fan assembly may include a constant torque motor. The negative air filtration system is designed to have reduced complexity and increased reliability when compared to existing negative air filtration systems.

CROSS REFERENCE TO A RELATED APPLICATION

The application claims the benefit of U.S. Provisional Application No.63/008,895 filed Apr. 13, 2020, the contents of which are herebyincorporated in their entirety.

BACKGROUND

Negative air machines are used to remove contaminants from the air of anenclosed space. For example, negative air machines may be used to removeasbestos, mold, and/or microbes from the air. Once the negative airmachine filters the contaminants from the air, depending on theconfiguration, the air may be either recycled within the space, orexhausted outside the space.

Negative air machines have been found to be particularly useful inhospital settings, where negative air machines are placed in particularrooms. Specifically, negative air machines have been used in varioustypes of isolation rooms (e.g., airborne infection isolation (AII)rooms, protective isolation/environment (PE) rooms, convertibleisolation rooms, and combination AII/PE rooms). By placing the negativeair machines in these rooms, the spread of infectious diseases may beprevented, or at least mitigated.

To remove the microbes from the air, traditional negative air machinesinclude a fan, at least one pre-filter, and a HEPA filter. The fan isused to create a negative pressure and draw air into the negative airmachine (e.g., through the inlet and out of the outlet). The pre-filteris used to remove larger particles and debris from the air (e.g., largedust particles, hair, etc.). The HEPA filter is used to remove smallerparticles from the air (e.g., the microbes). Commonly, the fan isdisposed at the inlet of the negative air machine, with one or more ofthe filters (e.g., the pre-filter and/or the HEPA filter) disposeddownstream of the fan. This generates a positive pressure across thefilter(s) downstream of the fan. This positive pressure may causeincreased stress on the filter(s) and/or on any seal around thefilter(s), which may result in a leak of contaminants (e.g., eitherthrough a hole in a filter or through an opening in a seal around afilter). If contaminants are able to leak through the negative airmachine then the negative air machine may not reliably prevent thespread of infectious diseases.

To reliably prevent the spread of infectious disease (e.g., toeffectively remove contaminants from the air), the filters of thenegative air machines need to remain unclogged. To help detect cloggedfilters microprocessors are commonly used. Traditionally,microprocessors are connected to the fan assembly (e.g., to the motorpowering the fan) to detect an increase in power consumption. Anincrease in power consumption may indicate that a filter is clogged andis in need of replacement. However, this use of microprocessors maycause an unnecessary dependence and may result in increased complexityfor manufacturing.

Accordingly, there remains a need for a negative air machine and methodof operating such negative air machine, that is effectively removescontaminants from the air, while also capable of being more easilymanufactured.

BRIEF DESCRIPTION

According to one embodiment, a negative air filtration system includinga housing, a pre-filter, a HEPA filter, and a fan assembly is provided.The housing includes an inlet and an outlet. The pre-filter is disposedwithin the housing, downstream of the inlet. The HEPA filter is disposedwithin the housing, downstream of the pre-filter. The fan assembly isdisposed within the housing, downstream of the HEPA filter. The fanassembly is in airflow communication with the pre-filter and the HEPAfilter. The fan assembly generates a negative pressure across thepre-filter and the HEPA filter.

In accordance with additional or alternative embodiments, the housingfurther includes an interior surface, wherein an insulation is disposedon the interior surface.

In accordance with additional or alternative embodiments, the insulationincludes an exterior foil surface and a fiberglass body.

In accordance with additional or alternative embodiments, the negativeair filtration system further includes a supply duct transition disposedon an upper surface of the housing, the supply duct transition includingan outlet flange and an outlet plate, wherein the outlet plate includesa plurality of apertures disposed therein.

In accordance with additional or alternative embodiments, the negativeair filtration system further includes a pressure switch, the pressureswitch operably connected to an indicator, the indicator disposed on thehousing.

In accordance with additional or alternative embodiments, the pressureswitch includes a tube, the tube including a first end and a second end,the first end disposed outside the housing and the second end disposedbetween the fan assembly and the HEPA filter.

In accordance with additional or alternative embodiments, the indicatoris configured to signal when at least one of the pre-filter and the HEPAfilter are in need of replacement.

In accordance with additional or alternative embodiments, the fanassembly includes a constant torque motor including an operating torque.

In accordance with additional or alternative embodiments, the constanttorque motor is operably connected to a selection device, the selectiondevice configured to adjust the operating torque.

In accordance with additional or alternative embodiments, operatingtorque correlates to an approximately constant RPM, wherein theapproximately constant RPM is between 800 and 1500 RPM.

In accordance with additional or alternative embodiments, the fanassembly includes a forward curved wheel blower.

In accordance with additional or alternative embodiments, the HEPAfilter includes an exterior perimeter, a sealing assembly disposed aboutthe exterior perimeter; the sealing assembly configured prevent a bypassaround the HEPA filter.

In accordance with additional or alternative embodiments, the sealingassembly includes at least one gasket and at least one planar member.

In accordance with additional or alternative embodiments, the negativeair filtration system further includes a mounting rail disposed withinthe housing, the mounting rail disposed adjacent the sealing assembly.

In accordance with additional or alternative embodiments, the inlet isdisposed on a lower surface of the housing and the outlet is disposed onan upper surface of the housing, the inlet and the outlet beingvertically oriented.

In accordance with additional or alternative embodiments, the negativeair filtration system further includes a plurality of wheels disposed onthe lower surface of the housing.

In accordance with additional or alternative embodiments, the lowersurface includes a surface area less 4 sq. ft.

According to another aspect of the disclosure a method for operating anegative air filtration system is provided. The negative air filtrationsystem including a pre-filter, a HEPA filter disposed downstream of thepre-filter, and a fan assembly including a constant torque motor, thefan assembly disposed downstream of the HEPA filter. The methodincluding a step for operating the negative air filtration system at afirst required CFM for a first environment, the constant torque motoroperating at a first approximately constant torque for the firstrequired CFM. The method further including a step for operating thenegative air filtration system at a second required CFM for a secondenvironment, the constant torque motor operating at a secondapproximately constant torque for the second required CFM.

In accordance with additional or alternative embodiments, the constanttorque motor includes a selection device configured to control theoperating torque of the constant torque motor between the firstapproximately constant torque and the second approximately constanttorque.

In accordance with additional or alternative embodiments, the firstapproximately constant torque and the second approximately constanttorque each respectively correlate to an approximately constant RPM, theapproximately constant RPM between 800 and 1500 RPM.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter, which is regarded as the disclosure, is particularlypointed out and distinctly claimed in the claims at the conclusion ofthe specification. The following descriptions of the drawings should notbe considered limiting in any way. With reference to the accompanyingdrawings, like elements are numbered alike:

FIG. 1 is a perspective view of a negative air filtration systemincluding a housing, a pre-filter, a HEPA filter, and a fan assembly inaccordance with one aspect of the disclosure.

FIG. 2 is a perspective view of the pre-filter, as shown in FIG. 1, withinsulation disposed on the interior surface of the housing in accordancewith one aspect of the disclosure.

FIG. 3 is a perspective view of the HEPA filter, as shown in FIG. 1,with wheels disposed on the lower surface of the housing in accordancewith one aspect of the disclosure.

FIG. 4 is a perspective view of a first embodiment of a supply ducttransition disposed on the upper surface of the housing in accordancewith one aspect of the disclosure.

FIG. 5 is a perspective view of a second embodiment of a supply ducttransition in accordance with one aspect of the disclosure.

FIG. 6 is a perspective view of a pressure switch in accordance with oneaspect of the disclosure.

FIG. 7 is a perspective view of an indicator and a dial disposed on thehousing in accordance with one aspect of the disclosure.

FIG. 8 is a perspective view of a fan assembly, as shown in FIG. 1, withthe fan assembly including a constant torque motor and a forward curvedwheel blower in accordance with one aspect of the disclosure.

FIG. 9 is a perspective view of a HEPA filter, as shown in FIG. 1,depicting the exterior perimeter of the HEPA filter in accordance withone aspect of the disclosure.

FIG. 10 is a perspective view of a sealing assembly disposed about theexterior perimeter shown in FIG. 9 in accordance with one aspect of thedisclosure.

FIG. 11 is a flow diagram illustrating a method of operating a negativeair filtration system in accordance with one aspect of the disclosure.

DETAILED DESCRIPTION

A negative air filtration system including a housing, a pre-filter, aHEPA filter, and a fan assembly, and a method of operating the negativeair filtration system are provided. The negative air filtration system,by disposing the fan assembly downstream of the HEPA filter and thepre-filter, generates a negative pressure across the pre-filter and theHEPA filter. By generating a negative pressure across the filters (e.g.,instead of a positive pressure), the negative air filtration system maymore reliably prevent the spread of infectious diseases (e.g., comparedto existing negative air filtration systems) by avoiding the generationof unneeded stress on the filters and the seal around the filters.Additionally, the negative air filtration system provided herein mayhave reduced complexity and be more easily manufactured (e.g., comparedto existing negative air filtration systems) by avoiding the use ofmicroprocessors to monitor the clogging of the filters. For example,instead of using microprocessors, the negative air filtration system mayuse a pressure switch to monitor the clogging of the filters. Althoughdescribed herein to be particularly useful in a hospital setting, itshould be appreciated that the negative air filtration system may beused within any environment that is in need of contaminant filtration(e.g., for home remediation, etc.).

With reference now to the Figures, an exemplary negative air filtrationsystem 100 is shown in FIG. 1. The negative air filtration system 100includes a housing 200, a pre-filter 300, a HEPA filter 400, and a fanassembly 500. The housing 200 including an inlet 210 and an outlet 220.The pre-filter 300 is disposed within the housing 200, downstream of theinlet 210. The HEPA filter 400 is disposed within the housing 200,downstream of the pre-filter 300. The fan assembly 500 is disposedwithin the housing 200, downstream of the HEPA filter. The fan assembly500 is in airflow communication with the pre-filter 300 and the HEPAfilter 400. Being in airflow communication may be interpreted to meanthat the airflow that is drawn into the negative air filtration system100 (e.g., by the fan assembly 500) is passed through the fan assembly500, the pre-filter 300, and the HEPA filter 400. The fan assembly 500generates a negative pressure across the pre-filter 300 and the HEPAfilter 400 (e.g., instead of a positive pressure).

The housing 200 includes an interior surface 230, which may includeinsulation 231. For example, the housing 200 may be made of one or morepieces of sheet metal joined together (e.g., using any known fasteningmeans) at the corners of the housing 200. The interior surface 230 ofthe housing 200 may be viewed as the inward facing surface of the piecesof sheet metal. In certain instances, the insulation 231 may line theentire interior surface 230 of the housing 200 to minimize noise outsidethe housing 200. It should be appreciated that, in certain instances,the insulation 231 lines only a portion of the interior surface 230 ofthe housing 200 (e.g., may only line the interior surface 230 near thefan assembly 500). As shown in FIG. 2, the insulation 231 may include anexterior foil surface 233 and a fiberglass body 232.

The pre-filter 300 may be disposed directly adjacent to the HEPA filter400. A perspective view of a pre-filter 300 installed within thenegative air filtration system 100 is shown in FIG. 2. This pre-filter300 may be easily removable and replaceable (e.g., if/when thepre-filter 300 becomes clogged). The pre-filter 300 may be used toremove larger particles (e.g., hair, dust, etc.) from the air enteringthe negative air filtration system 100 to avoid the larger particlesfrom clogging the HEPA filter 400. A perspective view of a negative airfiltration system 100 with the pre-filter 300 removed is shown in FIG. 3(e.g., with the HEPA filter 400 exposed). The HEPA filter 400 may beused to remove fine contaminants (e.g., microbes) from the air beforethe air is either recycled within the space (e.g., back into the room),or exhausted outside the space (e.g., outside of the room and/orbuilding).

When exiting the negative air filtration system 100, the air may bepassed through a duct (not shown). For ease of installation (e.g., tomake it easy to connect with the duct), the negative air filtrationsystem 100 may include a supply duct transition 600 (as shown in FIGS. 4and 5). The supply duct transition 600 may be disposed on an uppersurface 202 of the housing 200. The supply duct transition 600 mayinclude an outlet flange 610 and an outlet plate 620 containing aplurality of apertures. The outlet flange 610 may extendcircumferentially around the outlet plate 620. The outlet flange 610 mayextend substantially perpendicular from the upper surface 202 of thehousing 200. Substantially perpendicular may mean that the outlet flange610 and the upper surface 202 of the housing 200 may form an angle ofapproximately 90° (e.g., +/−5°). The outlet flange 610 may be sized toallow a duct to be configured over the outlet flange 610 (e.g., to allowthe duct to be clamped to the outside of the outlet flange 610). Theoutlet plate 620 may be configured in any fashion capable of allowingair to flow out of the negative air filtration system 100 and throughthe duct. A perspective view of a first embodiment of a supply ducttransition 600 with one potential outlet plate 620 configuration (e.g.,with the plurality of apertures having a circular geometry) is shown inFIG. 4. A perspective view of a second embodiment of a supply ducttransition 600 with another potential outlet plate 620 configuration(e.g., with the plurality of apertures configured as slots) is shown inFIG. 5.

To function efficiently and effectively remove contaminants from theair, the filters (e.g., the pre-filter 300 and the HEPA filter 400) ofthe negative air filtration system 100 need to remain unclogged. Tomonitor the status of the filters the negative air filtration system 100may include a pressure switch 700 (as shown in FIGS. 1 and 6). Thepressure switch 700 may be operably connected to an indicator 720 (e.g.,through one or more wired or wireless connections). The indicator 720may include any device capable of signaling (e.g., capable of generatinga sound and/or light). In certain instances, the indicator 720 is alight (e.g., an LED) disposed on the housing 200 (as shown in FIG. 7).The indicator 720 may be used by the negative air filtration system 100to signal (e.g., by flashing) when at least one of the pre-filter 300and the HEPA filter 400 are in need of replacement.

The pressure switch 700 may trigger the indicator 720 using a diaphragm(not shown). For example, the pressure switch 700 may have a flexiblediaphragm connected to a tube 710 (shown in FIG. 1). The diaphragm maymove relative to a change in pressure (e.g., triggering the indicator720). The tube 710 may include a first end 711 disposed outside thehousing 200 (e.g., open to atmosphere) and a second end 712 disposedinside the housing 200 (e.g., between the fan assembly 500 and the HEPAfilter 400). Thus, the pressure switch 700 may monitor a pressure changebetween the fan assembly 500 and the HEPA filter 400 and trigger theindicator 720 when the pressure drops to a point that is indicative of afilter (e.g., the pre-filter 300 or the HEPA filter 400) being cloggedto the point that it is in need of replacement. It should be appreciatedthat the configuration of a pre-filter 300 upstream of the HEPA filter400 may mitigate the HEPA filter 400 from becoming clogged with largerparticles (e.g., dust, hair, etc.). As mentioned above, clogged filtersmay affect the efficiency of the negative air filtration system 100. Forexample, a clogged filter may cause the fan assembly 500 to consume morepower.

A perspective view of an exemplary fan assembly 500 is shown in FIG. 8.As shown, the fan assembly 500 may include a constant torque motor 510and a forward curved wheel blower 520. This may mean that the fanassembly 500 may not use a constant CFM motor (e.g., which mayincorporate one or more microprocessor). The constant torque motor 510may be operably connected (e.g., through one or more wired or wirelessconnections) to a selection device 511 (e.g. a dial shown in FIG. 7).The selection device 511 may be configured to adjust the operatingtorque (e.g., which may correlate to an approximately constant RPM)between various approximately constant torques. An approximatelyconstant torque may mean that the torque does not vary substantiallyduring operation (e.g., +/−100 Nm from the set torque). For example, theselection device 511 may change the operating torque of the constanttorque motor 510 between a number (e.g., five or more) of differentpresent constant torques, which may not vary substantially duringoperation (e.g., without adjusting the dial 511). In certain instances,the approximately constant RPM for which the torque correlates to isbetween 800 and 1500 RPM. The selection device 511 may make it possibleto adjust the output (e.g., the CFM) of the fan assembly 500 based onthe size of the particular space that the negative air filtration system100 is being used in. For example, the selection device 511 may increasethe torque for a larger room and decrease the torque for a smaller room.Regardless of the size of the room, the fan assembly 500 may be used topull air through the HEPA filter 400 to remove contaminants (e.g.,microbes) from the air.

The negative air filtration system 100 may prevent air from bypassingthe HEPA filter 400. An exemplary embodiment of a HEPA filter 400 isshown in FIG. 9. As shown in FIG. 9, the HEPA filter 400 may include anexterior perimeter 410. The negative air filtration system 100 mayinclude a sealing assembly 800 disposed about the exterior perimeter 410(shown in FIG. 10). The sealing assembly 800 may include at least onegasket 820 (e.g., composed of a rubber or silicone material) and atleast one planar member 810 (e.g., composed of a sheet metal orplastic). The sealing assembly 800 is configured to prevent a bypassaround the HEPA filter 400. For example, the sealing assembly 800 may beconfigured in such a way that prevents any of the air that enters thenegative air filtration system 100 from passing through the outlet 220without first passing through the HEPA filter 400. In certain instances,the housing 200 includes a mounting rail 240 extending from the interiorsurface 230. The mounting rail 240 may be disposed adjacent to thesealing assembly 800 (e.g., in an overlapping manner, as shown in FIG.10).

The design and configuration of the negative air filtration system 100may make the negative air filtration system 100 easy to install and/ormove, which might be advantageous in environments where time is of theessence (e.g., in hospital settings). Additionally, the negative airfiltration system 100 may be designed in such a way that it's footprint(e.g., the amount of space required) is minimal. For example, thenegative air filtration system 100 may take up less than 4 square feetof floor space (e.g., the surface area of the lower surface 201 may beless than 4 square feet). This may be possible due to the orientation ofthe negative air filtration system 100. For example, the negative airfiltration system 100 may be configured to be vertically oriented (asshown in FIG. 1) where the outlet 220 is disposed on the upper surface202 and the inlet 210 is disposed on the lower surface 201. The negativeair filtration system 100 may include a plurality of wheels 250 disposedon the lower surface 201 of the housing 200. These wheels 250 may makeit possible to move the negative air filtration system 100 between rooms(e.g., from one hospital room to another).

As described above, the design and configuration of the negative airfiltration system 100 makes it possible to remove contaminants (e.g.,microbes) from air in an effective and reliable manner, with reducecomplexity (e.g., when compared to existing negative air machines thatincorporate microprocessors to monitor the filters). As mentioned,instead of using a constant CFM motor, the negative air filtrationsystem 100 described herein may utilize a constant torque motor 510connected to a selection device 511. This selection device 511 may makeit possible to operate the negative air filtration system 100 in amanner that is consistent with the needs of the environment in which itis being used.

The method 900 for operating a negative air filtration system 100 isshown in FIG. 11. This method 900 may be completed, for example, usingthe exemplary negative air filtration system 100 shown in FIGS. 1-10. Asdescribed above, the negative air filtration system 100 may include apre-filter 300, a HEPA filter 400 disposed downstream of the pre-filter300, and a fan assembly 500 including a constant torque motor 510. Thefan assembly 500 being disposed downstream of the HEPA filter 400. Themethod 900 includes step 910 for operating the negative air filtrationsystem 100 at a first required CFM for a first environment. The constanttorque motor 510 operating at a first approximately constant torque forthe first required CFM. The method 900 includes step 920 for operatingthe negative air filtration system 100 at a second required CFM for asecond environment. The constant torque motor 510 operating at a secondapproximately constant torque for the second required CFM. The adjustingof between the first approximately constant torque and the secondapproximately constant torque may be completed by adjusting theselection device 511. This selection device 511 may make it possible torelatively easily change the CFM of the negative air filtration system100 to match the particular needs of the environment (e.g., the room) inwhich it is being used. For example, this may remove the need of complexmodifications to the negative air filtration system 100 when moving thenegative air filtration system 100 from one room to another, whichultimately may save time.

The use of the terms “a” and “and” and “the” and similar referents, inthe context of describing the invention, are to be construed to coverboth the singular and the plural, unless otherwise indicated herein orcleared contradicted by context. The use of any and all example, orexemplary language (e.g., “such as”, “e.g.”, “for example”, etc.)provided herein is intended merely to better illuminate the inventionand does not pose a limitation on the scope of the invention unlessotherwise claimed. No language in the specification should be construedas indicating any non-claimed elements as essential to the practice ofthe invention.

While the present disclosure has been described with reference to anexemplary embodiment or embodiments, it will be understood by thoseskilled in the art that various changes may be made and equivalents maybe substituted for elements thereof without departing from the scope ofthe present disclosure. In addition, many modifications may be made toadapt a particular situation or material to the teachings of the presentdisclosure without departing from the essential scope thereof.Therefore, it is intended that the present disclosure not be limited tothe particular embodiment disclosed as the best mode contemplated forcarrying out this present disclosure, but that the present disclosurewill include all embodiments falling within the scope of the claims.

What is claimed is:
 1. A negative air filtration system comprising: ahousing comprising an inlet and an outlet; a pre-filter disposed withinthe housing, downstream of the inlet; a HEPA filter disposed within thehousing, downstream of the pre-filter; and a fan assembly disposedwithin the housing, downstream of the HEPA filter, the fan assembly inairflow communication with the pre-filter and the HEPA filter, the fanassembly generating a negative pressure across the pre-filter and theHEPA filter.
 2. The negative air filtration system of claim 1, whereinthe housing further comprises an interior surface, wherein an insulationis disposed on the interior surface.
 3. The negative air filtrationsystem of claim 2, wherein the insulation comprises an exterior foilsurface and a fiberglass body.
 4. The negative air filtration system ofclaim 1, further comprising a supply duct transition disposed on anupper surface of the housing, the supply duct transition comprising anoutlet flange and an outlet plate, wherein the outlet plate includes aplurality of apertures disposed therein.
 5. The negative air filtrationsystem of claim 1, further comprising a pressure switch, the pressureswitch operably connected to an indicator, the indicator disposed on thehousing.
 6. The negative air filtration system of claim 5, wherein thepressure switch comprises a tube, the tube comprising a first end and asecond end, the first end disposed outside the housing and the secondend disposed between the fan assembly and the HEPA filter.
 7. Thenegative air filtration system of claim 5, wherein the indicator isconfigured to signal when at least one of the pre-filter and the HEPAfilter are in need of replacement.
 8. The negative air filtration systemof claim 1, wherein the fan assembly comprises a constant torque motorcomprising an operating torque.
 9. The negative air filtration system ofclaim 8, wherein the constant torque motor is operably connected to aselection device, the selection device configured to adjust theoperating torque.
 10. The negative air filtration system of claim 9,wherein operating torque correlates to an approximately constant RPM,wherein the approximately constant RPM is between 800 and 1500 RPM. 11.The negative air filtration system of claim 8, wherein the fan assemblycomprises a forward curved wheel blower.
 12. The negative air filtrationsystem of claim 1, wherein the HEPA filter comprises an exteriorperimeter, a sealing assembly disposed about the exterior perimeter, thesealing assembly configured prevent a bypass around the HEPA filter. 13.The negative air filtration system of claim 12, wherein the sealingassembly comprises at least one gasket and at least one planar member.14. The negative air filtration system of claim 12, further comprising amounting rail disposed within the housing, the mounting rail disposedadjacent the sealing assembly.
 15. The negative air filtration system ofclaim 1, wherein the inlet is disposed on a lower surface of the housingand the outlet is disposed on an upper surface of the housing, the inletand the outlet being vertically oriented.
 16. The negative airfiltration system of claim 15, further comprising a plurality of wheelsdisposed on the lower surface of the housing.
 17. The negative airfiltration system of claim 15, wherein the lower surface comprises asurface area less 4 sq. ft.
 18. A method for operating a negative airfiltration system comprising a pre-filter, a HEPA filter disposeddownstream of the pre-filter, and a fan assembly comprising a constanttorque motor, the fan assembly disposed downstream of the HEPA filter,the method comprising: operating the negative air filtration system at afirst required CFM for a first environment, the constant torque motoroperating at a first approximately constant torque for the firstrequired CFM; and operating the negative air filtration system at asecond required CFM for a second environment, the constant torque motoroperating at a second approximately constant torque for the secondrequired CFM.
 19. The method of claim 18, wherein the constant torquemotor comprises a selection device configured to control the operatingtorque of the constant torque motor between the first approximatelyconstant torque and the second approximately constant torque.
 20. Themethod of claim 18, wherein the first approximately constant torque andthe second approximately constant torque each respectively correlate toan approximately constant RPM, the approximately constant RPM between800 and 1500 RPM.